98 lines
2.2 KiB
Perl
98 lines
2.2 KiB
Perl
|
package UNIVERSAL;
|
||
|
|
|
||
|
|
# UNIVERSAL should not contain any extra subs/methods beyond those
|
||
|
|
# that it exists to define. The use of Exporter below is a historical
|
||
|
|
# accident that should be fixed sometime.
|
||
|
|
require Exporter;
|
||
|
|
*import = \&Exporter::import;
|
||
|
|
@EXPORT_OK = qw(isa can);
|
||
|
|
|
||
|
|
1;
|
||
|
|
__END__
|
||
|
|
|
||
|
|
=head1 NAME
|
||
|
|
|
||
|
|
UNIVERSAL - base class for ALL classes (blessed references)
|
||
|
|
|
||
|
|
=head1 SYNOPSIS
|
||
|
|
|
||
|
|
$io = $fd->isa("IO::Handle");
|
||
|
|
$sub = $obj->can('print');
|
||
|
|
|
||
|
|
$yes = UNIVERSAL::isa($ref, "HASH");
|
||
|
|
|
||
|
|
=head1 DESCRIPTION
|
||
|
|
|
||
|
|
C<UNIVERSAL> is the base class which all bless references will inherit from,
|
||
|
|
see L<perlobj>
|
||
|
|
|
||
|
|
C<UNIVERSAL> provides the following methods
|
||
|
|
|
||
|
|
=over 4
|
||
|
|
|
||
|
|
=item isa ( TYPE )
|
||
|
|
|
||
|
|
C<isa> returns I<true> if C<REF> is blessed into package C<TYPE>
|
||
|
|
or inherits from package C<TYPE>.
|
||
|
|
|
||
|
|
C<isa> can be called as either a static or object method call.
|
||
|
|
|
||
|
|
=item can ( METHOD )
|
||
|
|
|
||
|
|
C<can> checks if the object has a method called C<METHOD>. If it does
|
||
|
|
then a reference to the sub is returned. If it does not then I<undef>
|
||
|
|
is returned.
|
||
|
|
|
||
|
|
C<can> can be called as either a static or object method call.
|
||
|
|
|
||
|
|
=item VERSION ( [ REQUIRE ] )
|
||
|
|
|
||
|
|
C<VERSION> will return the value of the variable C<$VERSION> in the
|
||
|
|
package the object is blessed into. If C<REQUIRE> is given then
|
||
|
|
it will do a comparison and die if the package version is not
|
||
|
|
greater than or equal to C<REQUIRE>.
|
||
|
|
|
||
|
|
C<VERSION> can be called as either a static or object method call.
|
||
|
|
|
||
|
|
=back
|
||
|
|
|
||
|
|
The C<isa> and C<can> methods can also be called as subroutines
|
||
|
|
|
||
|
|
=over 4
|
||
|
|
|
||
|
|
=item UNIVERSAL::isa ( VAL, TYPE )
|
||
|
|
|
||
|
|
C<isa> returns I<true> if the first argument is a reference and either
|
||
|
|
of the following statements is true.
|
||
|
|
|
||
|
|
=over 8
|
||
|
|
|
||
|
|
=item
|
||
|
|
|
||
|
|
C<VAL> is a blessed reference and is blessed into package C<TYPE>
|
||
|
|
or inherits from package C<TYPE>
|
||
|
|
|
||
|
|
=item
|
||
|
|
|
||
|
|
C<VAL> is a reference to a C<TYPE> of perl variable (er 'HASH')
|
||
|
|
|
||
|
|
=back
|
||
|
|
|
||
|
|
=item UNIVERSAL::can ( VAL, METHOD )
|
||
|
|
|
||
|
|
If C<VAL> is a blessed reference which has a method called C<METHOD>,
|
||
|
|
C<can> returns a reference to the subroutine. If C<VAL> is not
|
||
|
|
a blessed reference, or if it does not have a method C<METHOD>,
|
||
|
|
I<undef> is returned.
|
||
|
|
|
||
|
|
=back
|
||
|
|
|
||
|
|
These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>.
|
||
|
|
If you want simple local access to them you can do
|
||
|
|
|
||
|
|
*isa = \&UNIVERSAL::isa;
|
||
|
|
|
||
|
|
to import isa into your package.
|
||
|
|
|
||
|
|
=cut
|